Smelting method for ZG13Cr9Mo2Co1NiVNbNB material steel casting based on same-steel-grade return scraps

Abstract

The invention discloses a smelting method of a ZG13Cr9Mo2Co1NiVNbNB material steel casting based on return scraps of the same steel grade. The smelting method sequentially comprises the steps of intermediate frequency furnace smelting, VOD (Vacuum Oxygen Decarburization) furnace refining, LF (Ladle Furnace) furnace refining and VD (Vacuum Degassing) furnace refining. During intermediate frequency furnace smelting, the adding cost is reduced, and alloy component fluctuation is reduced; vOD refining is conducted, ferroboron is added under the high vacuum of 67 Pa, and oxygen and nitrogen pollution is isolated; meanwhile, nitrogen is introduced for increasing nitrogen in the VD stage, nitrogen or argon is switched according to a nitrogen content detection value, inclusions are avoided, and the nitrogen content is accurately controlled; and the yield of chromium is remarkably improved, and the smelting time is shortened.

Description

Technical Field

[0001] This invention relates to the field of casting technology, and specifically to a method for melting ZG13Cr9Mo2Co1NiVNbNB steel castings based on recycled materials of the same steel grade. Background Technology

[0002] ZG13Cr9Mo2Co1NiVNbNB (CB2) is a new type of 9%~12%%Cr ferritic heat-resistant steel. This steel grade is mainly produced by adding Co and B elements to E911 while removing W elements. Co reduces the precipitation of σ ferrite, while B is dissolved in the material matrix and can inhibit the growth of M23C6 carbides, thereby improving the material's durability. This material has excellent thermal conductivity and oxidation resistance, a low coefficient of thermal expansion, and good resistance to intergranular corrosion and stress corrosion, making it a primary material for manufacturing key cast steel components for 620℃ ultra-supercritical steam turbines.

[0003] The required chemical composition (mass percentage) of ZG13Cr9Mo2Co1NiVNbNB material is as follows: C: 0.10~0.14%, Si: 0.20~0.30%, Mn: 0.80~1.00%, P: ≤0.015%, S: ≤0.010%, Cr: 9.00~9.60%, Mo: 1.40~1.60%, V: 0.18~0.23%, Co: 0.90~1.10%, Ni: 0.10~0.20%, Nb: 0.05~0.08%, B: 0.008~0.011%, Mn: 0.80~1.00%, N: 0.015~0.025%, Al: The material properties are ≤0.020%, with extremely high requirements for performance indicators and strict quality requirements. Not only is the steel composition complex with numerous alloying elements, including polluting elements such as Co, easily oxidized elements such as B, and gaseous elements such as N, but the required range is also narrow, making chemical composition control very difficult and smelting very challenging.

[0004] CN111304520B discloses a method for smelting CB2 material in an electric arc furnace, which adopts a combination process of EAF furnace, LF furnace, VD furnace and LF furnace. The EAF furnace smelting of this material results in a large amount of chromium oxidation, low chromium alloy recovery rate and high production cost. At the same time, the use of ferrochrome nitride to supplement nitrogen increases quality risk and production cost.

[0005] CN104911453A discloses a process for preparing high-temperature resistant cast steel material with a temperature of 620 degrees Celsius. The process adopts a combination of EAF furnace and LF furnace. In the LF furnace, nitrogen is blown to replace ferrochromium nitride to supplement nitrogen to the target range. Simply blowing nitrogen can easily exceed the target value range, thereby making the molten steel supersaturated. During casting, nitrogen precipitates and forms pores; at the same time, deoxidation products remain.

[0006] Therefore, this application is submitted. Summary of the Invention

[0007] The purpose of this invention is to provide a method for melting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade. The method involves melting in an induction furnace, refining in a VOD furnace, refining in an LF furnace, and refining in a VD furnace in sequence. This method eliminates the need to add ferrochromium oxide for nitrogen supplementation, shortens the melting time, improves the chromium yield, and solves the problems existing in the prior art.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following solution: A method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade includes the following steps: S1, the same type of return material and pure iron material consistent with the finished steel castings are used as the furnace charge of the medium frequency furnace. Slag is laid before charging, the furnace charge is arranged during charging, and after all the furnace charge is melted, an alloy that is not easy to oxidize is added. When the temperature of the molten steel reaches ≥1650℃, the steel is tapped into the VOD furnace for oxygen blowing and decarburization. S2. When the temperature of the molten steel reaches 1600℃~1620℃, vacuum is drawn. The initial decarburization is carried out in sequence by pre-blowing oxygen, the deep decarburization is carried out by main blowing oxygen, the residual carbon is removed by deep vacuum, and deoxidizer and slag are added to reduce the molten steel. After maintaining the vacuum at 67Pa for ≥10min, the vacuum is broken, the temperature is measured and sampled for testing, and the steel is tapped into the LF furnace to reduce oxygen and adjust the composition. S3, under nitrogen conditions, preliminary deoxidation and reducing slag formation are carried out. After white slag is formed, samples are taken to test the oxygen and nitrogen content. When the oxygen content is below 20 ppm, the main alloy is added, and the main alloying elements and secondary alloying elements are adjusted to the internal control range in turn. The oxygen content is tested again. When it is below 20 ppm, ferroboron is added to adjust the boron content to the internal control range. When the nitrogen content exceeds the limit, argon is switched to gas. When the composition of each alloy meets the internal control range, the steel temperature is adjusted to 1630℃~1650℃ and the steel is tapped into the VD furnace for nitrogen replenishment. S4. After the molten steel is in place, adjust the argon pressure, draw a deep vacuum, maintain the vacuum degree below 67Pa for more than 12 minutes, break the vacuum and measure the temperature and take samples. Continuously analyze whether the nitrogen content is within the internal control middle limit or below the internal control lower limit. Choose whether to perform soft blowing of argon or nitrogen to make the molten steel temperature reach 1575℃~1580℃ before pouring and casting to obtain the finished steel casting.

[0009] Existing methods for smelting cast steel parts using electric arc furnace (EAF), LF furnace refining, VD furnace refining, and LF furnace refining involve high-temperature electric arcs in the EAF furnace leading to significant chromium oxidation (oxidation rate >15%), requiring excessive addition of ferrochrome nitride for compensation. This new method utilizes induction melting in a medium-frequency furnace, electromagnetic stirring to reduce steel exposure, and pre-laying of alkaline slag (active lime and fluorite) to inhibit oxidation. Combined with furnace charge layout to reduce oxygen, this eliminates the need for ferrochrome nitride, reducing its addition cost and minimizing alloy composition fluctuations. While EAF high-temperature oxidizing slag adsorbs boron (B), B readily combines with oxygen during LF refining. This method employs VOD refining, adding ferroborone under a high vacuum of 67 Pa to isolate oxygen and nitrogen contamination. Simultaneously, nitrogen is introduced during the VD stage to increase nitrogen content, ensuring pure gas nitrogen addition without foreign impurities. During the VD stage, nitrogen or argon is dynamically switched based on nitrogen content detection values, allowing for coordinated control of nitrogen content and steel purity as the steel reaches its tapping and casting temperature. This prevents impurities after tapping and also removes excess nitrogen, preventing porosity during casting.

[0010] Furthermore, the weight ratio of recycled steel to pure iron feedstock of the same grade is 6~7:2~3; The slag material consists of quicklime and fluorite, with quicklime accounting for 0.5% to 1.0% of the total amount of molten steel and fluorite accounting for 15% to 20% of the quicklime.

[0011] Furthermore, during charging, small pieces of furnace charge are located at the bottom of the furnace, medium and large pieces of furnace charge are located at the edge of the bottom of the furnace, and small pieces of material are filled in the gaps between the large pieces of furnace charge.

[0012] Furthermore, the alloys that are not easily oxidized are low-carbon ferrochrome, nickel plate, and ferromolybdenum, which are added in batches. The contents of Cr, Ni, and Mo are adjusted to the lower limit of the internal control, and the C content is controlled to 0.25%~0.40%.

[0013] Further, in step S2, after vacuuming, the vacuum degree reaches 6000~7000Pa for pre-blowing oxygen, with an oxygen flow rate of 0.20~0.30Nm3 / min·t; the main oxygen flow rate is 0.35~0.50Nm3 / min·t, and oxygen blowing is stopped when the oxygen potential curve and exhaust gas temperature begin to decrease; deep vacuuming is performed, and deoxidizer and slag are added when the oxygen potential curve decreases. The deoxidizer includes 0.2~0.5kg / t aluminum granules and a mixture of 1.0~1.5kg / t low-carbon ferrosilicon and calcium silicon.

[0014] Furthermore, the nitrogen pressure in step S3 is 0.2~0.25MPa. Aluminum particles and calcium silicate particles are added for deoxidation during the initial decarburization. Then, active lime and fluorite are added in batches with a total amount of 5~10kg / t, with each addition not exceeding 100kg. During this process, the Si content is controlled within the internal control range.

[0015] Furthermore, the main alloy consists of ferromolybdenum, ferrocobalt, electrolytic nickel, ferrochrome, and ferrovanadium added in sequence, while the secondary alloying elements are Mn, Si, C, and Nb.

[0016] Furthermore, when the nitrogen content reaches 0.025%~0.030%, argon gas is switched to gas.

[0017] Furthermore, in step S4, when the temperature of the molten steel reaches 1575℃~1580℃, if the N content is 0.015%~0.020%, continue to gently blow argon gas for at least 5 minutes; if the N content is below 0.015%, switch from argon gas to nitrogen gas until the N content is 0.015%~0.020%, and then gently blow argon gas again for at least 3 minutes. The soft blowing process maintains the slag layer undulation and prevents the molten steel from being exposed.

[0018] Furthermore, nitrogen gas is purged at least once.

[0019] The beneficial effects of this invention are as follows: This method uses induction melting in a medium-frequency furnace, electromagnetic stirring to reduce steel exposure, and pre-laying alkaline slag (active lime and fluorite) to inhibit oxidation. It eliminates the need for adding ferrochrome nitride, reducing its addition cost and minimizing alloy composition fluctuations. While EAF high-temperature oxidizing slag adsorbs boron, boron readily combines with oxygen during LF refining. This method employs VOD refining, adding ferroborone under a high vacuum of 67 Pa to isolate oxygen and nitrogen contamination. Simultaneously, nitrogen is introduced during the VD stage to increase nitrogen content. The VD stage switches between nitrogen and argon based on nitrogen content detection values, ensuring coordinated control of nitrogen content and steel purity during the steel's journey to the tapping / casting temperature. This prevents impurities after tapping and also removes excess nitrogen, avoiding porosity during casting. This significantly improves chromium recovery and shortens smelting time. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process flow of the smelting method of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0023] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. Example

[0024] This invention provides a method for melting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade, referring to... Figure 1 The specific smelting method includes the following steps: (1) Induction furnace smelting Batching: The same type of return material and pure iron material that are consistent with the finished steel castings are used as the furnace charge of the medium frequency furnace. The same type of return material is the gating system, risers, padding and scrap castings. The weight ratio of the same type of return material to pure iron material is 6~7:2~3. Slag spreading: Before charging, spread active lime and fluorite at the bottom of the induction furnace to create alkaline slag to protect the molten steel and reduce oxidation. The amount of lime is 0.5% to 1.0% of the total amount of molten steel, and the amount of fluorite is 15% to 20% of the amount of active lime.

[0025] Charging: Small pieces of the same type of returned material and pure iron are placed at the bottom of the furnace, while medium and large pieces are placed at the edge of the bottom. Small pieces are filled between the large pieces of material to ensure that the charge is compacted.

[0026] Electric Melting: After charging is complete, electricity is applied for melting. High-power, rapid melting is used initially to minimize oxygen absorption during the melting process. Temperature measurement and sampling begin when approximately 80% of the charge has melted. If the content of elements such as P, Ni, Nb, V, Cr, Mo, and Co in the molten steel is not higher than the internal control upper limit, charging continues until all the charge has melted. Samples are then taken again for chemical composition analysis. The slag viscosity is adjusted according to the slag condition. Then, slag is skimmed off and new basic slag is created, with a slag layer thickness not exceeding 60mm. Then, non-oxidizing alloys, namely low-carbon ferrochrome, nickel plate, and ferromolybdenum, are added in batches. The Cr, Ni, and Mo content is adjusted to the internal control lower limit, and the C content is controlled to 0.25%~0.40%. When the molten steel temperature reaches ≥1650℃, it is tapped into a VOD furnace for oxygen decarburization.

[0027] This method uses an induction furnace to melt various raw materials to provide molten steel for roughing. Induction furnace melting requires strict control of the quality of the raw materials, with strict control over the P content to be ≤0.013%, and the content of residual elements such as As, Sb, Sn, and Cu not exceeding the internal control upper limit. Because the content range of Ni, V, and Nb is very narrow, it needs to be controlled below the internal control lower limit during batching.

[0028] (2) VOD furnace refining Pre-oxygen blowing (preliminary decarburization): After the molten steel is transferred into the VOD furnace and reaches the work station, argon gas is turned on and slag is removed. The temperature of the molten steel is measured and controlled to 1600℃~1620℃. Then, the cover is closed and a vacuum is drawn to make the vacuum degree in the furnace reach 6000~7000Pa before pre-oxygen blowing begins.

[0029] Main oxygen blowing (deep decarburization): The flow rate of pre-blown oxygen is controlled at 0.20~0.30 Nm. 3 / min·t, then lower the oxygen lance, the oxygen lance height is 1.1~1.2m, then main oxygen blowing.

[0030] Deep vacuum: The oxygen flow rate in the main blowing oxygen is controlled at 0.35~0.50 Nm. 3 At a rate of / min·t, observe the oxygen potential curve and exhaust gas temperature. If both are normal, raise the oxygen lance and stop blowing oxygen when the oxygen potential curve and exhaust gas temperature begin to decrease. Continue deep vacuuming for decarbonization and observe changes in the oxygen potential curve.

[0031] Adding deoxidizer and slag to reduce molten steel: After the oxygen potential curve decreases, add deoxidizer and slag to reduce the molten steel. Then, maintain at 67 Pa for more than 10 minutes, followed by vacuum breaking, temperature measurement, and sampling to detect chemical composition and oxygen content. The deoxidizer here is 0.2~0.5 kg / t aluminum granules, 1.0~1.5 kg / t low-carbon ferrosilicon, and calcium silicate deoxidizer; the slag includes 5~10 kg / t active lime and fluorite, where the weight ratio of active lime to fluorite is 10:1.

[0032] In VOD furnace refining, oxygen potential diagrams and exhaust gas temperature are standard techniques in this field and will not be elaborated upon here.

[0033] (3) LF furnace refining Nitrogen purging: The molten steel refined in the VOD furnace is transferred into the LF furnace, and nitrogen gas is turned on at the same time. The nitrogen pressure is controlled at 0.2~0.25MPa. According to the O and Si content in the molten steel, an appropriate amount of aluminum particles and silicon-calcium particles are added as deoxidizers for deoxidation. Then, according to the viscosity and thickness of the slag layer, 5~10kg / t of active lime and fluorite are added. The active lime and fluorite are added in batches, and the amount added each time does not exceed 100kg. During this process, the Si content needs to be controlled so that it does not exceed the internal control limit.

[0034] Oxygen testing: After white slag is formed, samples are taken to test the oxygen and nitrogen content. When the oxygen content is below 20 ppm, the chemical composition is adjusted. According to the difference between the actual composition and the target composition, the main alloys, namely ferromolybdenum, ferrocobalt, electrolytic nickel, ferrochrome, and ferrovanadium, are added in sequence to adjust the content of the main alloying elements Mo, Co, Ni, Cr, and V to the internal control range. Then, the content of the secondary alloying elements Mn, Si, C, and Nb is adjusted to the internal control range.

[0035] Secondary oxygen test: Test the oxygen content again. If the oxygen content is below 20 ppm, add ferric boron to adjust the B content to the internal control range. If the oxygen content exceeds 20 ppm, add deoxidizer to deoxygenate to below 20 ppm.

[0036] The entire LF furnace melting time is maintained at 40-60 minutes. When the nitrogen content reaches 0.025%-0.030%, the nitrogen gas is replaced with argon gas. After all components meet the internal control requirements, the molten steel temperature is adjusted to 1630-1650℃, and then the steel is tapped for VD furnace refining and nitrogen replenishment.

[0037] (4) VD furnace refining The molten steel refined in the LF furnace is transferred into the VD furnace. The argon pressure inside the furnace is adjusted to 0.1~0.15MPa. Then, the furnace is covered and a deep vacuum is drawn. The vacuum degree is maintained below 67Pa for more than 12 minutes. Then, the vacuum is broken and the temperature is measured and a sample is taken to determine the nitrogen content in the molten steel.

[0038] Argon blowing: If the detected N content is between 0.015% and 0.020%, continue to blow argon gas for more than 5 minutes. During the soft blowing of argon gas, the slag layer is observed to undulate but the molten steel does not turn red. Argon bubbles rise and adsorb inclusions, while preventing secondary oxidation of the molten steel.

[0039] Nitrogen replenishment: If the N content is below 0.015%, switch from argon to nitrogen until the N content is within acceptable limits (0.015%~0.020%, which is the internal control limit). Nitrogen molecules dissociate and dissolve at the steel interface: N2(g)→2[N]. The dissolution rate is positively correlated with the surface area of ​​the bubbles. Continue to gently blow argon for more than 3 minutes to remove excess nitrogen and avoid nitrogen precipitation during casting, which can cause porosity. During the gentle blowing of argon, slag layer undulations are observed, but the steel does not turn red, to prevent secondary oxidation of the steel.

[0040] Finally, after the molten steel reaches a temperature of 1575~1580℃, it is tapped and poured to obtain the finished cast steel part, with the following composition: C: 0.110%~0.137%, Si: 0.218%~0.289%, Mn: 0.830%~0.948%, P: 0.0123%~0.0143%, S: 0.0007%~0.0039%, Cr: 9.18%~9.48%, Mo: 1.45%~1.55%, Ni: 0.125%. The composition is as follows: ~0.189%, Al: 0.003%~0.014%, Co: 0.95%~1.10%, Nb: 0.055%~0.071%, V: 0.191%~0.219%, B: 0.0086%~0.0109%, N: 0.0160%~0.0209%, O: 0.015%~0.0027%, with the remainder being iron; the yield of Cr is ≥97%, and the yield of B is 75%~80%. Other properties are shown in Table 1, and all properties meet the standard requirements.

[0041] Table 1 Performance Test Table of Finished Cast Steel Parts Smelted by This Method Comparative Example A comparative example using existing processes: recycled steel and pure iron of the same grade are sequentially smelted in an electric arc furnace (EAF), refined in an LF furnace, refined in a VD furnace, and then refined again in an LF furnace to produce cast steel parts. The resulting cast steel parts require nitrogen supplementation with ferrochrome nitride during the VD furnace refining process, with the ferrochrome nitride addition ratio being 1.5%–2.0%. The chromium recovery rate in the finished cast steel parts is 86%–92%, and the boron recovery rate is 55%–68%, significantly lower than that obtained by the method described above. The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade, characterized in that, The steps are as follows: S1, the same type of return material and pure iron material consistent with the finished steel castings are used as the furnace charge of the medium frequency furnace. Slag is laid before charging, the furnace charge is arranged during charging, and after all the furnace charge is melted, an alloy that is not easy to oxidize is added. When the temperature of the molten steel reaches ≥1650℃, the steel is tapped into the VOD furnace for oxygen blowing and decarburization. S2. When the temperature of the molten steel reaches 1600℃~1620℃, vacuum is drawn. The initial decarburization is carried out in sequence by pre-blowing oxygen, the deep decarburization is carried out by main blowing oxygen, the residual carbon is removed by deep vacuum, and deoxidizer and slag are added to reduce the molten steel. After maintaining the vacuum at 67Pa for ≥10min, the vacuum is broken, the temperature is measured and sampled for testing, and the steel is tapped into the LF furnace for deoxidation and composition adjustment. S3, under nitrogen conditions, preliminary deoxidation and reducing slag formation are carried out. After white slag is formed, samples are taken to test the oxygen and nitrogen content. When the oxygen content is below 20 ppm, the main alloy is added, and the main alloying elements and secondary alloying elements are adjusted to the internal control range in turn. The oxygen content is tested again. When it is below 20 ppm, ferroboron is added to adjust the boron content to the internal control range. When the nitrogen content exceeds the limit, argon is switched to gas. When the composition of each alloy meets the internal control range, the steel temperature is adjusted to 1630℃~1650℃ and the steel is tapped into the VD furnace for nitrogen replenishment. S4. After the molten steel is in place, adjust the argon pressure, draw a deep vacuum, maintain the vacuum degree below 67Pa for more than 12 minutes, break the vacuum and measure the temperature and take samples. Continuously analyze whether the nitrogen content is within the internal control middle limit or below the internal control lower limit. Choose whether to perform soft blowing of argon or nitrogen to make the molten steel temperature reach 1575℃~1580℃ before pouring and casting to obtain the finished steel casting.

2. The method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade according to claim 1, characterized in that, The weight ratio of recycled steel to pure iron in the same steel grade is 6~7:2~3; The slag material consists of quicklime and fluorite, with quicklime accounting for 0.5% to 1.0% of the total amount of molten steel and fluorite accounting for 15% to 20% of the quicklime.

3. The method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade according to claim 1, characterized in that, During charging, small pieces of furnace charge are located at the bottom of the furnace, medium and large pieces of furnace charge are located at the edge of the bottom of the furnace, and small pieces of material are filled in the gaps between the large pieces of furnace charge.

4. The method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade according to claim 1, characterized in that, The alloys that are not easily oxidized are low-carbon ferrochrome, nickel plate, and ferromolybdenum, which are added in batches. The contents of Cr, Ni, and Mo are adjusted to the lower limit of the internal control, and the C content is controlled to 0.25%~0.40%.

5. The method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade according to claim 1, characterized in that, In step S2, after evacuation, the vacuum level reaches 6000~7000Pa, and oxygen is pre-blown at a flow rate of 0.20~0.30Nm. 3 / min·t; the oxygen flow rate of the main oxygen blowing system is 0.35~0.50Nm³ / min·t. 3 / min·t, observe the oxygen potential curve and stop blowing oxygen when the exhaust gas temperature begins to drop; deep vacuum, add deoxidizer and slag when the oxygen potential curve drops. The deoxidizer includes 0.2~0.5kg / t aluminum granules and a mixture of 1.0~1.5kg / t low carbon ferrosilicon and calcium silicon.

6. The method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade according to claim 1, characterized in that, In step S3, the nitrogen pressure is 0.2~0.25MPa. During the initial decarburization, aluminum particles and calcium silicate particles are added for deoxidation. Then, active lime and fluorite are added in batches, with a total amount of 5~10kg / t, and each addition not exceeding 100kg. During this process, the Si content is controlled within the internal control range.

7. A method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade, as described in claim 6, is characterized in that... The main alloy consists of ferromolybdenum, ferrocobalt, electrolytic nickel, ferrochrome, and ferrovanadium added in sequence, while the secondary alloying elements are Mn, Si, C, and Nb.

8. A method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade, as described in claim 6, is characterized in that... When the nitrogen content reaches 0.025%~0.030%, switch to argon gas.

9. A method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade, as described in claim 6, is characterized in that... In step S4, when the temperature of the molten steel reaches 1575℃~1580℃, if the N content is 0.015%~0.020%, continue to gently blow argon gas for at least 5 minutes; if the N content is below 0.015%, switch from argon gas to nitrogen gas until the N content is 0.015%~0.020%, then gently blow argon gas again for at least 3 minutes. The soft blowing process maintains the slag layer undulation and prevents the molten steel from being exposed.

10. A method for smelting ZG13Cr9Mo2Co1NiVNbNB cast steel parts based on recycled materials of the same steel grade, as described in claim 9, is characterized in that... Nitrogen gas must be purged at least once.

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